This invention refers to a method and an equipment for producing a uniformly moist veneer or plywood.
In manufacturing veneer the intention is to achieve a uniformly moist veneer after dryer. This will succeed only, if the veneer is dried to complete dryness, i.e. to a moisture content of 0%. A drawback of a completely dry veneer is that it is brittle and breaks easily. In order to avoid this, the veneer is usually dried on an average to a moisture content of about 5%. Hereby the moisture content of individual veneers will vary in the range of 0 to 15%.
A moisture meter for veneer is a generally known device. In some special cases it is also known to use moistening of veneer, but then the whole veneer is moistened, and any local moisture differences are not taken into consideration. Also moistening of plywood is known.
The object of the present invention is to produce a uniformly moist veneer or plywood, which can be achieved according to the invention in such a way that the moisture of the veneer or plywood is measured in one or several points, and any moisture differences noticed in this veneer or plywood are levelled in a moistening stage following said measuring, in which stage the veneer or plywood, based upon measuring results received, is moistened with water or steam in one or several points in order to achieve an adjusted uniform moisture content. This can be carried out by bringing to each point such an amount of water or steam, which is based upon the measuring result of said point, or alternatively the average moisture content of said veneer or plywood is calculated based upon the measuring results of said veneer or plywood, and based upon said average value the veneer or plywood is moistened to an adjustable level.
Moistening of the veneer or plywood can be carried out for instance by spraying water and/or steam on surface or surfaces of the veneer or plywood. Another way of moistening is to eject or spread water at one or both surfaces of the veneer or plywood.
Moisture measuring can be carried out either only at one side of the veneer or alternatively at both sides, whereby a still more exact information of local moisture variations of the veneer. Based upon the measuring results the moistening can in the same way be carried out either only at one side of the veneer or at both sides, regardless the moisture measuring was carried out only at one side or at both sides. Moistening both sides will guarantee a more uniform penetration of water into the veneer.
Moisture measuring and moistening can be arranged anywhere at the veneer manufacturing line after the dryer or possibly already before the dryer.
The equipment according to the invention comprises:
a moisture meter arranged to measure moisture of a veneer or a plywood at one or more points;
a moistening device comprising a plurality of independently adjustable moistening dies positioned down streams the moisture meter and extending across direction of motion of the veneer or plywood;
moisture measuring electronics connected to the moisture meter, and
a control system arranged to regulate the separate moistening dies of the moistening device based on impulses from the moisture measuring electronics.
The moisture meter may extend either along the grain of the veneer or across the grain. The moistening device has preferably as much moistening dies as the number of measuring points in the moisture meter, so that each moistening die is controlled by measuring results received from a measuring point of the moisture meter, which measured that part of the veneer or plywood, which comes into the area of influence of said moistening die.
The equipment may independently have moisture measuring points and/or moistening dies either only for one side or for both sides of the veneer.